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Check Unnecessary Nullable Parameters


This command was removed in 1.18.0 and is no longer available.

Consider migrating to "dcm check-parameters".

Checks unnecessary nullable parameters in functions, methods, constructors. Removing unnecessary nullables can help reduce amount of checks in the code.

To execute the command, run:

$ dcm check-unnecessary-nullable lib # or dcm un lib

Full command description:

Usage: dcm check-unnecessary-nullable [arguments] <directories>
-h, --help Print this usage information.

-r, --reporter=<console> Analysis output format.
[console (default), json, codeclimate, gitlab, checkstyle]
-a, --absolute-path Show absolute paths in console reporter output.
--json-path=<path/to/file.json> Path to the JSON file with the analysis output.

-c, --print-config Print resolved config.

--root-folder=<./> Root folder.
(defaults to the current directory)
--sdk-path=<directory-path> Dart SDK directory path.
If the project has a `.fvm/flutter_sdk` symlink, it will be used if the SDK is not found.
--exclude=<{**/*.g.dart,**/*.freezed.dart}> File paths in Glob syntax to be exclude.
(defaults to "{**/*.g.dart,**/*.freezed.dart}")

--no-congratulate Don't show output even when there are no issues.

--verbose Show verbose logs.

--ci-key The license key to run on CI server. Can be provided via DCM_CI_KEY env variable.
--email The email used to purchase the license. Can be provided via DCM_EMAIL env variable.

--no-analytics Disable sending anonymous usage statistics.

--monorepo Include publicly exported code into the check.

--[no-]fatal-found Treat found unnecessary nullable parameters as fatal.
(defaults to on)

Suppressing the command

In order to suppress the command add the ignore: unnecessary-nullable comment. To suppress for an entire file add ignore_for_file: unnecessary-nullable to the beginning of a file.

Monorepo support


By default, this command treats all code that is exported from the package as used. It uses check-exports-completeness results and won't report even transitive public entities that are not exported directly.

This command also follows this convention of locating implementation files in the lib/src/ folder. If you don't follow this convention, you will need to pass the --monorepo flag for this command to work.

To disable this behavior use --monorepo flag. This might be useful when all the packages in your repository are only used within the repository and are not published to the pub.

Overriding monorepo mode for a particular package

To override the monorepo mode for a particular package, set the monorepo entry in the analysis_options.yaml.

For example, if publicly exported files of a particular package are not expected to be changed, setting the monorepo entry to false and passing the --monorepo option will enable the monorepo mode for all other packages, but not the one with monorepo: false.

Output example


Use --reporter=console to enable this format.



The reporter prints a single JSON object containing meta information and the unnecessary nullable parameters. Use --reporter=json to enable this format.

The root object fields are

  • formatVersion - an integer representing the format version (will be incremented each time the serialization format changes)
  • timestamp - a creation time of the report in YYYY-MM-DD HH:MM:SS format
  • unnecessaryNullable - an array of unnecessary nullable issues
"formatVersion": 2,
"timestamp": "2021-04-11 14:44:42",
"unnecessaryNullable": [

The unnecessaryNullable object fields are

  • path - a relative path of the file with unnecessary nullable parameters declaration
  • issues - an array of issues detected in the target class
"path": "lib/src/some/class.dart",
"issues": [

The issue object fields are

  • declarationName - the name of a declaration with unnecessary nullable parameters
  • declarationType - the type of a declaration with unnecessary nullable parameters (function, method or constructor)
  • parameters - an array of strings representing parameters that are marked as nullable
  • offset - a zero-based offset of the class member location in the source
  • line - a zero-based line of the class member location in the source
  • column - a zero-based column of class member the location in the source
"declarationName": "someFunction",
"declarationType": "function",
"parameters": "[String? value]",
"offset": 156,
"line": 7,
"column": 1


Reports unnecessary nullable issues in merge requests based on Code Quality custom tool. Use --reporter=gitlab to enable this format.


Use --reporter=checkstyle to enable this format.

<?xml version="1.0"?>
<checkstyle version="10.0">
<file name="../abstract_class.dart">
<error line="0" severity="warning" message="function myFunction has unnecessary nullable parameters" source="unnecessary-nullable-issue"/>
<file name="../class_with_factory_constructors.dart">
<error line="0" severity="warning" message="function myOtherFunction has unnecessary nullable parameters" source="unnecessary-nullable-issue"/>